FR2723777A1 - POWER TRANSMISSION TRAIN OF AN AUTOMATIC TRANSMISSION FOR VEHICLE - Google Patents

Abstract

The invention relates to a power transmission train of an automatic transmission for a vehicle, which comprises a device (2, 4) for performing a continuous shifting maneuver in the region of low speed, directly connecting the transmission train. transmission of power to the output shaft (8) of the engine (E) so as to reduce the impulses due to shocks of gear changes, and reducing the number of one-way clutches so as to simplify the whole structure.

Description

Power transmission train of an automatic transmission for

vehicle

BACKGROUND OF THE INVENTION

  The present invention relates to a power transmission train

  an automatic transmission for a vehicle.

  In general, an automatic transmission of a vehicle comprises a transmission control unit which automatically controls a plurality of clutches and brakes mounted in a gear train so as to adjust the ratio between the planetary gears according to the speed and the charge. Although the power transmission train should normally include a planetary compound unit and at least five friction elements to produce four ratios for forward speeds and one ratio for reverse speeds, it is necessary to improve more efficient shifting, a planetary gear unit, seven friction elements and three one-way clutches. This results in a complicated construction of the power transmission train and

increases weight.

  In addition, the conventional automatic transmission includes a limited number of gearshift phases, which means that pulses caused by shocks from gearshifts inevitably appear and the range of gearshifts is also restricted due to the number limited gear ratios, making it difficult to obtain an optimal ratio of fuel to power performance. In addition, the pulses caused by shocks due to speed changes frequently appear due to the high input torque and frequent speed change maneuvers in the low speed range. In addition, the input shaft and the gear train must be directly connected to each other in the high speed range to improve the efficiency of the power transmission. But the classic transmission does not include

no such means.

SUMMARY OF THE INVENTION

  An object of the present invention is to provide a power transmission train of an automatic transmission for a vehicle comprising means for effecting a continuous gear change in the region of low speeds of

  so as to reduce the impulses coming from shocks due to speed changes.

  Another object of the present invention is to provide a power transmission train of an automatic transmission for a vehicle which directly connects a gear train to the output end of an engine so as to

  improve the efficiency of power transfer.

  Yet another object of the present invention is to provide a power transmission train which can simplify the structure of the power transmission train of an automatic transmission of a vehicle by reducing the number of

  one-way clutches and friction elements.

  According to an embodiment of the present invention, a power transmission train of an automatic transmission of a vehicle comprises: a casing for installing the automatic transmission; a torque converter for changing the speed torque of engine power; a hull cover for enclosing the torque converter; a first gear change section of a compound planetary gear unit comprising first and second simple planetary gear units mounted on an input shaft for performing a first gear change operation, the first simple planetary gear unit comprising a first sun wheel surrounded by and in engagement with a plurality of first pinions supported by a first planet carrier, a first ring of planetary gear surrounding the first pinions and internally engaged with them, and a hub connected to the first ring of planetary gear, and the second single planetary gear unit comprising a second sun wheel surrounded by a plurality of second gears and engaged with them, supported by a second planet carrier, and a second ring of planetary gear surrounding the second gears and in taken internally with them; a second gear changing section of a single planetary gear unit comprising a third and a fourth simple planetary gear units for performing a second gear shifting operation, the third simple planetary gear unit comprising a third sun wheel surrounded by a plurality of third pinions supported by a third planet carrier and engaged with them, and a third ring of planetary gear surrounding the third pinions and internally engaged with them, and the fourth unit with single planetary train 1o comprising a fourth solar wheel surrounded by a plurality of fourth pinions supported by a fourth planet carrier and engaged therewith, and a fourth ring of planetary gear surrounding the fourth pinions and internally engaged therewith; a plurality of power transfer elements for transferring engine power; and a differential gear for transferring the output of the second gear change section to the axle of a vehicle, in which the first sun gear is selectively locked by a friction element mounted on the transmission case to serve as an input or reaction element, the second ring of planetary gear is connected to the first sun wheel selectively locked by a friction element to serve as an input or reaction element, the first and second pinions are connected to each other via a first power transfer member for transferring the gear change ratio of the first gear change section via a fourth power transfer member, the third crown of planetary gear is connected to a fourth power transfer element, the fourth solar wheel is connected to receive r the output of the third single planetary gear unit and blocked by a clutch to be prevented from turning in the opposite direction to the direction of rotation of the motor, the third sun wheel is blocked by a friction element serving as a reaction element, and the third single planetary gear unit is selectively locked by a friction element to provide the same speed as the first section

gear change.

BRIEF DESCRIPTION OF THE DRAWINGS

  The present invention will now be described more specifically and

  only by way of example with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram showing the power transmission train of an automatic transmission according to an embodiment of the present invention; FIG. 2 is a graph showing the relationships between the torques of the turbine and the stator and the output speed of a continuous and automatic speed change mode in the automatic transmission of FIG. 1; FIG. 3 is a graph showing the relationship between the output torque of the automatic transmission of the invention and the output speed of a continuous and automatic gear change mode; Figure 4 is a graph schematically describing the speeds of the automatic transmission of the invention by analogy with a lever; FIG. 5 is a graph comparing the distribution of the ratios between gears of the automatic transmission of the invention with that of a conventional five-speed automatic transmission; FIG. 6 is a table showing the combination of the working elements of the automatic transmission of the invention according to the speed change stages; FIG. 7 is a diagram schematically showing the power transmission train of an automatic transmission according to a second mode of

  realization of the present invention.

  FIG. 8 is a diagram schematically showing the power transmission train of an automatic transmission according to a third embodiment of the present invention; FIG. 9 is a diagram schematically showing the power transmission train of an automatic transmission according to a fourth embodiment of the present invention; and FIG. 10 is a diagram schematically showing the transmission train of an automatic transmission according to a fifth embodiment of

the present invention.

  The present invention will now be described more specifically and

  only by way of example with reference to the accompanying drawings.

  DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

  Referring to Figure 1, the power transmission train of an automatic transmission according to a first embodiment of the present invention comprises a torque converter TC driven by a motor E, a first shift section 2 d '' a planetary gear unit to transform the torque of the torque converter by suitable gear ratios, and a second gear change section 4 of a planetary gear unit to further reduce the gear ratios of the first gear section 2. The torque converter TC comprises a drive element I connected directly to the crankshaft of the engine E, a turbine T mounted opposite the drive element and driven by oil, and a stator S arranged between the drive element I and the turbine T to modify the direction of the oil flow and assist the rotation of the element d 'training. The torque converter TC can

  have the same structure as that described in US Patent No. 3,613,479.

  A shell cover 6 connects the drive element I to the motor E, and includes a friction element C 1 for directly transferring the power of the motor to a first shaft 8 (input shaft). The first shaft 8 is connected via a hub 14 to a first planetary gear ring 12 of the first gear changing section 2. The internal surface of the first planetary gear ring is engaged with a plurality of first pinions 16 which, for their part, are engaged with a first sun wheel 18 disposed between them. The first pinions 16 are operatively connected via a first power transfer element 20 to a plurality of second pinions 22, which in turn are engaged with a second sun wheel 24. The second pinions 22 are engaged with the internal surface of a second planetary gear ring 26 which is connected in operation via a second power transfer element 28 to the first solar wheel 18. A second friction element BI is provided for selectively blocking the second power transfer element 28 so that the first sun wheel 18 and the second sun gear 26 serve as reaction elements. The hub 14 is selectively blocked by a third friction element B2 so that the first planetary gear ring 12 serves as a reaction element, so that when the second sun wheel 24 serves as an input element, the first power transfer 20 is driven in rotation anticlockwise with respect to the motor, that is to say in the opposite direction to that of the input,

  so as to make the vehicle reverse.

  The second solar wheel 24 is connected via a third power transfer element 30 to the turbine T. The first power transfer element 20 which connects the first and second pinions 16 and 22 is connected via a fourth power transfer element 32 to the stator S of the torque converter. To selectively receive the torque from the stator S, the fourth power transfer element 32 is provided with a fourth friction element C2 for connection with a fifth power transfer element 34 which is directly connected to the stator S. The fifth power transfer element 34 is provided with a first one-way clutch F1 to prevent the stator S from rotating counter-clockwise relative to the engine. It is preferable to provide a shock absorber 36 between the hub 14 and the first planetary gear ring 12 to reduce the shock which takes place when the first friction element C1 is

  used to connect the first shaft 8 with the motor.

  A drive transfer chain sprocket 38 is mounted on the fourth power transfer member 32 to transfer reduced speed through a chain 42 to a driven transfer chain sprocket 40 to transfer movement to the second shifting section 4, which consists of a third unit with a single planetary gear 44 receiving the movement of the drive transfer chain pinion 38, the movement of which is in turn transferred to a fourth unit with a single planetary gear 46. The third single planetary gear unit 44 includes a third planetary gear ring 48 operatively connected to the driven transfer chain sprocket 40 and the chain 42, a plurality of third sprockets 50 engaged with the interior of the third gear ring planet 48, and a third sun wheel 52 in engagement with the third pinions which surround it. The third sun wheel 52 is designed to be blocked by a fourth friction element C3 so as to rotate in one piece with the third pinions 50, and by a sixth friction element B3 mounted on the casing 56 of the transmission to serve selectively of reaction element. In addition, a second one-way clutch F2 is provided on the transmission casing 56 to prevent the third sun wheel 52 from turning anti-clockwise relative to the engine, so that the third sun wheel 52 is rotated in the same direction

than the engine.

  The third planet carrier 58 which supports the third pinions 50 is provided for transferring the torque to a fourth sun wheel 60 from the fourth unit with a planetary gear 46. The periphery of the fourth sun wheel 60 is engaged with the fourth pinions 62 which are supported by a fourth planet carrier 64 operatively connected to a differential gear D. In addition, the fourth pinions 62 are engaged with the interior of a fourth planetary gear ring gear 66 fixedly mounted on the housing 56 of the transmission. The fourth planetary gear unit 46 produces the final gear ratio applied to the gear

  differential D to rotate the axle 68 of the vehicle.

  Thus, the operation of the engine causes the drive element I of the torque converter TC, which is connected via the cover 6 of the shell to the output shaft of the engine, to turn and eject the oil. contained in the torque converter to the turbine. Then, the rotational force of the turbine is transferred via the third power transfer element 30 to the second solar wheel 24 of the first speed change section 2. In this case, the stator S of the torque converter TC is prevented from turning in the opposite direction to that of the engine under the effect of the first one-way clutch F1, thereby increasing the torque of the torque converter. The torque of the turbine T is transferred via the third power transfer element 30 to the second sun wheel 24 to rotate the second pinion 32 counterclockwise when looking from the side of the engine. However, in the ranges "N" and "P" which are shown in FIG. 6, no element works, so that the

  motor power is not output.

  When the shift lever (not shown) is brought to the forward range "D", the transmission control unit causes the second friction element B1 of the first shift section 2 to lock the first sun wheel 18 and the second planetary gear ring 26 of the first planetary gear unit 2. Next, the second sun wheel 24 serves as an input element and the second planetary gear ring 26 serves as a reaction element, so the

  fourth power transfer element 32 serves as an output element.

  The relationships between gears can be described by analogy with a lever as shown in Figure 4. It is assumed that the left end of a lever L represents the first node Ni consisting of the first sun wheel 18 and the second crown of planetary gear 26, a first point adjacent the second node N2 of the first and fourth power transfer elements 20 and 32, a second point adjacent the third node N3 of the first ring of planetary gear 12, and the right end the fourth node N4 of the second solar wheel 24. Thus, the

  fourth node N4 becomes the entry point and the first node NI the fixed point.

  Then, a straight line L1 of arbitrary length is drawn vertically from the fourth node N4 to represent the amount of input speed. Then a connecting line L2 is drawn to connect the upper end of the input speed line L1 to the first node N1. Now, for example, if the shortest line L3 is drawn between the second node N2 and the connecting line L2, the line L3 becomes the output speed line at the second node N2. Therefore, the gear ratio can be expressed by the fraction between input speed line / output speed line (L1 / L3) which is

  considered to represent the ratio between gears of the first gear.

  The gear ratio of the first gear is transferred via the fourth power transfer element 32 to the pinion 38 to the drive transfer chain which in turn transfers the movement via the chain 42 to the pinion to transfer chain driven 40 and therefore to the second speed changing section 4. Then the transferred speed is again transferred via the third single planetary gear unit 44 to the fourth sun wheel 60 of the fourth single planetary gear unit 46, then is finally reduced by the reaction of the fourth planet gear ring 66. The

  finally reduced speed is provided by the fourth planet carrier 64.

  Similarly, the relationships between gears of the third unit with a single planetary gear can also be described by analogy with a lever represented by the reference symbol 'T "1" on the right side of FIG. 4. In this case, it is assumed that the left end of the lever "'T'" represents the fifth node N5 consisting of the third planet gear ring 48, the first point adjacent the sixth node N6 of the third planet carrier 44, and the right end the seventh node N7 of the third solar wheel 52. The torque of the first gear change section 2 is applied as input to the fifth node N5 which is assumed to have at its maximum the length of a line L3 arbitrarily drawn vertically from the fifth node N5. The line L4 which connects the upper end of the line L3 to the seventh node N7 represents the rate of reduction of the exit, so that the shortest line L5 between the sixth node N6 and the line L4 represents the speed of exit from the third single planetary gear unit 44 which is also reduced via the fourth single planetary gear unit 46 and finally transferred by the fourth planet carrier 64 to the differential gear D. Next, the driving axle 62 of

  vehicle is rotated.

  In the first gear, the final gear ratio is obtained by passing sequentially through the multiple stages of the first gear shift section 2, the drive and driven transfer chain sprockets, and the second gear shift section 4 In this case, although the third solar wheel 52 is locked in one direction under the effect of the second one-way clutch F2, the engine brake is not kept in operation when disengaged and the sixth friction element B3 is therefore operated manually to maintain the engine brake. When the speed of the stator S reaches a predetermined value or when the torque converter TC reaches the coupling condition, the transmission control unit operates the fourth friction element C2 so as to directly connect the stator S to the fourth power transfer element 32. As the torque of the stator S is added to the first speed of the fourth power transfer element 32, the rotational speed of the drive transfer chain sprocket 38 is increased more than the first speed. Thus, the torque of the turbine T is reduced by the amount transferred from the stator S to the drive transfer chain sprocket 38 in

  decreasing the total output torque.

  This represents a condition of continuous speed change before loading speed up to second speed, where the relationship between the output speed and the torque is shown in Figures 2 and 3. The continuous speed change maneuver begins just when the torque of the stator S is transferred to the first drive transfer chain sprocket 38. In this case, the torque of the drive element is kept constant, but the torque of the turbine is reduced while increasing the torque of the stator. When the output speed increases, the speed of the transmission torque is reduced, so that the gear change maneuver is performed continuously until the torque converter returns to the coupling condition, where the gear shift ratio is determined automatically based on the vehicle load. A lightly loaded vehicle causes the torque converter to reach i5 the coupling condition in a relatively short period of time, which shortens the time required to directly connect the stator S to the fourth power transfer element 32, while a heavily loaded vehicle causes the torque converter to reach the coupling condition over a period of time

  relatively long, which lengthens the maneuver in the region of low speed.

  In such a speed change mode, when the fourth friction element C2 is released to eliminate the torque coming from the stator S to the fourth power transfer element 32, the speed change is immediately carried out towards the first speed mode for increase the torque, which results in a sharp reduction in speed. Furthermore, when the stator S is connected to the fourth power transfer element 32, this causes the stator to receive reverse torque as in the case of stalling of the motor, so that the speed of the stator S is reduced and that the torque of the turbine T is increased, which results in an increase in the total torque to obtain a small reduction in speed. At this point, no shock due to the change of speed takes place, but the pulses due to the shocks which can appear during the connection or the disconnection of the stator with the fourth element of transfer of power 32 by means of the fourth element of friction C2 are absorbed by the torque converter TC I1 which acts as a shock absorber because the stator S is contained in the torque converter TC. In this case, the final ratio between the gears is obtained by passing sequentially through the multiple stages of the first gear change section 2, the drive and driven transfer chain sprockets, and the second gear change section 4 Naturally, no engine brake is maintained during

a walk in disengaged.

  According to this automatic continuous speed change mode, if the stator speed S reaches a predetermined value or if the torque converter TC reaches a coupling condition with increase in vehicle speed, the transmission control unit releases the second friction element BI and operates the first friction element CI. Thus, the output of the motor is transferred via the first friction element C1 to the first shaft 8 and to the first planetary gear ring gear 12 of the compound planetary gear unit 2, and via the third element power transfer 30 to the second solar wheel 24. The result is that the planetary compound unit 2 receives the power of the

two input elements.

  Therefore, as shown in FIG. 4, the first and fourth nodes N1 and N4 of the first speed change section 2 serve as an input terminal, and the output speed of the first speed change section 2 can therefore be represented by the straight line L8 drawn vertically between the second node N2 and the line L7 connecting the upper ends of the input speed lines LI and L6. Consequently, the compound planetary gear unit 2 is directly connected to the motor so as to produce the gear ratio of the second speed, where the second speed change section 4 determines a reduction in speed as in the case of the first gear. More specifically, the first friction element C1 directly connects the planetary gear unit 2 to the motor, thus producing a high power transfer efficiency, since the first friction element C1 is not used, the stator S turns at vacuum, which results in zero loss of the torque converter TC. This speed change is carried out when there is practically no difference, or only a very small difference, between the speeds of the turbine T and of the third planetary gear ring gear 48 and the speed of the

  motor, thus minimizing the impulses due to shock by the gear change.

  Naturally the vibrations which can be transferred to the hub 14 are absorbed by the shock absorber 36. The final ratio between gears of the second speed is obtained by passing sequentially through the multiple stages of the direct connection of the first speed change section 2 and of the motor, the drive and driven transfer chain sprockets, and the second gear shift section 4. When the vehicle speed is increased, the transmission control unit additionally activates the fourth friction element C2 of the first shift section 2 and the fifth friction element C3 of the second shift section 4, so that the first and second shift sections are directly connected to the motor to produce the gear ratio third gear. So the output speed of the first speed change section 2 can be represented by the line L8 emitted

  output by the second speed change section 4, without any modification.

  In this case, the motor is directly connected to the torque converter with all the elements of the first and second shift sections 2 and 4, and the optimal efficiency of the power transfer is therefore ensured and the engine brake can be maintained in the case of a walk in disengaged. In addition, the impulses due to the

  shock gear changes are very small due to the low torque of the motor.

  As shown in FIG. 6, the engine brake can be kept in the range "'1" during disengaged operation because the fourth and sixth friction elements C2 and B3 are used. Similarly, in the range "II" of the continuous and automatic speed change mode, the engine brake can be maintained due to the use of the fourth and sixth friction elements C2 and B3. In addition, in the range "L", the engine brake can be maintained because the second and sixth elements of

  friction B1 and B3 operate to block the first solar wheel 18. We have described below

  above the gear change maneuver when walking forward. As shown in Figure 5, the automatic transmission of the invention has a gear ratio of the first speed which is the same as that of a conventional five-speed automatic transmission, and performs continuous automatic gear changes until fourth gear ratio, thus avoiding impulses due to shocks changes in speed in the low speed region where serious impulses due to shocks from the

gear switch.

  When the gearshift lever is placed in the reverse range "R", the transmission control unit activates the third friction element B2 of the first gearshift section 2 and the sixth friction element B3 the second speed-changing section 4, so that the second sun wheel 24 of the planetary gear unit 2 serves as an input element, that the first planetary gear ring 12 serves as a reaction element, and that the fourth power transfer element 32 serves as an output element. Then, as shown in Figure 4, the ratio between gears for reverse gear can be represented by the straight line L10 which is drawn vertically between the second node N2 and the line L9 which connects the upper end of the speed line input L1 at the third node N3. The gear ratio in the case of reverse gear is transferred via the drive transfer chain sprockets and driven 38 and 40 to the second shift section 4, which is further reduced by the third single planetary gear unit and by the fourth planetary gear ring gear 66, and finally transferred to the differential gear D. When you need to stay in second gear, for example when the drive wheels spin on slippery roads, the unit of the transmission control operates the second and fifth friction elements B1 and C3 so that the first gear change section 2 makes a gear change to the first gear and that the second gear change section 4 is connected directly to the motor, so as to form relationships between different gears between the first and second speeds of the second gear changing section esse 4, as shown in dotted lines in FIG. 4. This speed mode maintains the engine brake during disengaging, and can also be used when the gearshift lever is placed in the "II" range. The friction elements are selectively combined according to the gear change ratios, as shown on

  the table of figure 6, where the small circles indicate the selection of the elements.

  As described above, the advantages of the automatic transmission of the invention are summarized as follows: 1) The gear change is carried out automatically and continuously, especially in the region of low speed where the operating time is short and o the impulses due to the speed change shock occur

  a lot, thus improving the speed change maneuver.

  2) In the region of high speeds where the pulses due to speed change shocks can be ignored but which requires a high power transfer efficiency, the speed change mechanism is directly

  connected to the engine by maximizing fuel efficiency.

  3) The number of friction elements and one-way clutches is reduced compared to the conventional automatic transmission,

  but improved operation, which reduces production costs and weight.

  Another embodiment of the present invention which is shown in Figure 7 shows a slightly different structure from the second gear change section 4, but the first gear change section 2 has the same structure as in Figure 1 To be more precise, the difference between the two embodiments is that one end of the third planet carrier 58 is connected to the fourth planet gear ring 66 and the fourth sun wheel 60 is fixedly connected to the casing 56 of the transmission. The speed change operation is the same as in the first embodiment. The operation of the first gear is carried out continuously. The second one-way clutch F2 engages the third sun gear 52 in the second gear, while the fifth friction element C3 is used to completely rotate the single planetary gear unit 44 in the third gear. When reversing, the sixth friction element B3 is used to prevent the sun wheel 52 from turning in the same direction as the motor, so that the sun wheel acts as a reaction element and thus reduces the speed. Referring to Figure 8, a third embodiment of the present invention shows a second shift section 4 consisting of a single single planetary gear unit. A fourth simple planetary gear unit included in the two previous embodiments has been omitted. More specifically, the third solar wheel 52 is connected via a sixth power transfer element 70 to the driven transfer chain sprocket 40. The third sprockets 50 are in common with the periphery of the third solar wheel 52 located between them, supported by the third planet carrier 58, one end of which is connected via the fifth friction element C3 to the sixth power transfer element 70 and the other end of which is connected to the gear differential D. The third planetary gear ring 48 surrounding and engaging therein with the third pinions 50 selectively serves as a reaction element using the sixth friction element B3 which is prevented from turning in the counterclockwise direction d '' a watch with respect to the engine thanks to the second one-way clutch F2. The present embodiment performs the same maneuver of

  gear change than the previous ones.

  A fourth embodiment of the present invention which is shown in FIG. 9 consists of the first gear change section 2, the structure of which is the same as in the first embodiment, and in the second gear change section 4 comprising the third and fourth simple planetary gear units 44 and 46 of the first and second embodiments. The third single planetary gear unit 44 comprises, as in the case of the third embodiment, the third sun wheel 52 which is connected via the sixth power transfer element 70 to the driven transfer chain pinion 40. The third pinions 50 are in common with the periphery of the third sun wheel 52 lying between them, supported by the third planet carrier 58, one end of which is connected via the fifth friction element C3 to the sixth transfer element of power 70. The third planetary gear ring 48 which surrounds and is internally engaged with the third pinions 50 serves selectively as a reaction element by using the sixth friction element B3 mounted on the casing 56 of the transmission and prevented from turning counterclockwise to the engine using the second one-way clutch nel F2. In addition, the other end of the third planet carrier 58 is connected to the fourth sun wheel 60, the periphery of which is in common with the fourth pinions 62 supported by the fourth planet carrier 64, which transfers the final gear ratio. to the differential gear D. The fourth planetary gear ring gear 66 which surrounds and engages inside with the fourth pinions 62 is fixedly mounted on the

  transmission case 56 to serve as a reaction element.

  The fifth embodiment of the present invention which is shown in Fig. 10 comprises a second shift section 4 consisting of two simple planetary gear units as in the fourth embodiment. The difference between the fourth and fifth embodiments is that the third planet carrier 58 is connected to the fourth planetary gear ring 66 to serve as an input element of the fourth single planetary gear unit 46, while connecting the fourth solar wheel 60 to the casing 56 of the transmission to serve as a reaction element. The present embodiment performs the same change maneuver.

faster than the previous ones.

Claims (12)

  1. Power transmission train of an automatic transmission of a vehicle comprising: a transmission casing (56) for installing said automatic transmission; a torque converter (TC) for modifying the speed of the power torque of a motor (E); a shell cover (6) for containing said torque converter; a first gear change section (2) of a planetary gear unit comprising first and second simple planetary gear units mounted on an input shaft (8) for performing a first gear change operation, said first single planetary gear unit comprising a first sun wheel (18) surrounded by and engaged with a plurality of first pinions (16) supported by a first planet carrier, a first planetary gear crown (12) surrounding and engaged at the interior with said first pinions, and a hub (14) connected to said first planetary gear ring gear, and said second single planetary gear unit comprising a second sun wheel (24) surrounded by and in   taken with a plurality of second pinions (22) supported by a second holder   satellites, and a second planetary gear ring (26) surrounding and internally engaged with said second pinions; a second gear change section (4) of a single planetary gear unit comprising third and fourth simple planetary gear units for performing a second gear change operation, said third simple planetary gear unit comprising a third sun wheel (52) surrounded by and engaged with a plurality of third pinions (50) supported by a third planet carrier (58), and a third planetary gear ring (48) surrounding and engaged therein with said third pinions , and said fourth single planetary gear unit comprising a fourth sun wheel (60) surrounded by and engaged with a plurality of fourth pinions (62) supported by a fourth planet carrier (64), and a fourth planetary gear ring ( 66) surrounding and engaging inside with said fourth pinions; a plurality of power transfer elements (32, 34) for transferring the power of said motor (E); and a differential gear (D) for transferring the output of said second gear change section to an axle (68) of the vehicle, wherein said first sun gear (12) is selectively locked by a friction element (B2) mounted on said transmission casing (56) to serve as an input or reaction element, the second sun gear (26) is connected to said first sun wheel (18) selectively locked by a friction element (BI1 ) to serve as an input or reaction element, said first and second pinions (16; 22) are connected to each other by means of a first power transfer element (20) to transfer the ratio between gears of said first gear changing section (2) via a fourth power transfer element (32), said third sun gear (48) is connected to a fourth element power transfer (32), said fourth solar wheel (60) is connected so as to receive the output of said third single planetary gear unit   (44) and blocked by a clutch to be prevented from turning in the opposite direction to -   direction of rotation of said motor, said third sun wheel (52) is blocked by a friction element (B3) to serve as a reaction element, and said third single planetary gear unit is selectively blocked by a friction element (C3) to provide the same speed as said first speed change section 2. Power transmission train for an automatic transmission according to claim 1, in which a friction element is provided for selectively connecting said second planet carrier to the stator (S) of said torque converter (TC) for transferring the torque of said stator (S) to a transfer chain sprocket drive (38).   3. Power transmission train for an automatic transmission according to claim 1, in which said second sun wheel (24) is operatively connected to the turbine (T) of said torque converter (TC) and said second planetary gear ring (26). ) is blocked by a friction element (BI) so that   said second sun wheel (24) delivers a first speed forward.   4. Power transmission train of an automatic transmission according to claim 1, in which a friction element is provided for connecting said third planet carrier (58) to the power transfer element for transferring the   torque of said third sun wheel (52) and reach the third speed mode.   5. Power transmission train of an automatic transmission according to claim 1, in which a friction element (B3) is provided for blocking said third planetary gear ring (48) to serve as reaction element. 6. An automatic transmission power transmission train for a vehicle comprising: a transmission casing (56) for installing said automatic transmission; a torque converter (TC) for changing the speed of the engine power torque; a shell cover (6) for containing said torque converter (TC); a first gear change section (2) of a planetary gear unit comprising first and second simple planetary gear units mounted on an input shaft (8) for performing a first gear change operation, said first single planetary gear unit comprising a first sun wheel (18) surrounded by and engaged with a plurality of first pinions (16) supported by a first planet carrier, a first planetary gear crown (12) surrounding and engaged at the interior with said first pinions (16), and a hub (14) connected to said first planetary gear ring gear (12), and said second single planetary gear unit comprising a second sun wheel (24) surrounded by and engaged with a plurality of second pinions (22) supported by a second planet carrier, and a second planetary gear ring (26) surrounding and engaged therein with said second pigs nons (22); a second gear change section of a single planetary gear unit (4) comprising third and fourth simple planetary gear units for performing a second gear shifting operation, said third simple planetary gear unit comprising a third sun wheel (52) surrounded by and engaged with a plurality of third pinions (50) supported by a third planet carrier (58), and a third planetary gear ring (48) surrounding and engaged therein with said third pinions (50), and said fourth single planetary gear unit comprising a fourth sun wheel (60) surrounded by and engaged with a plurality of fourth pinions (62) supported by a fourth planet carrier (64), and a fourth ring of planetary gear surrounding and engaged therein with said fourth pinions (62); a plurality of power transfer elements (32, 34) for transferring power from said motor; and a differential gear (D) for transferring the output of said second shift section (4) to an axle (68) of the vehicle, wherein said third single planetary gear unit (48, 50, 52) reduces or simply transfers the output of said first shift section (2), and said fourth planetary gear unit (60, 62, 64, 66) rotates said third planet carrier (58) in the same direction as said motor (E ) finally reducing the output of said train unit simple planetary.   7. The power transmission train of an automatic transmission according to claim 6, wherein said first and second sections of   gear change (2, 4) include separate shafts.   8. Power transmission train of an automatic transmission for a vehicle comprising: a transmission casing (56) for installing said automatic transmission; a torque converter (TC) for changing the speed of the engine power torque; a shell cover (6) for containing said torque converter; a first gear change section of a compound planetary gear unit (2) comprising first and second simple planetary gear units mounted on an input shaft (8) for performing a first gear change operation, said first single planetary gear unit comprising a first sun wheel (18) surrounded by and engaged with a plurality of first pinions (16) supported by a first planet carrier, a first planetary gear crown (12) surrounding and engaged at the interior with said first pinions, and a hub (14) connected to said first planetary gear ring gear (12), and said second single planetary gear unit comprising a second sun wheel (24) surrounded by and   engaged with a plurality of second pinions (22) supported by a second holder   satellites, and a second planetary gear ring (26) surrounding and internally engaged with said second pinions (22); a second gear change section of a single planetary gear unit (4) comprising third (44) and fourth (46) simple planetary gear units for performing a second gear change operation, said third planetary gear unit single comprising a third sun wheel (52) surrounded by and engaged with a plurality of third pinions (50) supported by a third planet carrier, and a third ring of planetary gear (48) o0 surrounding and engaged therein with said third pinions (50), and said fourth single planetary gear unit comprising a fourth sun wheel (60) surrounded by and in engagement with a plurality of fourth pinions (62) supported by a fourth planet carrier (58), and a fourth planetary gear ring (66) surrounding and engaging therein with said fourth pinions; a plurality of power transfer elements (32, 34) for transferring the power of said motor (E); and a differential gear (D) for transferring the output of said second gear change section (4) to an axle (68) of the vehicle, wherein said third sun gear (48) receives the output of said first gear section gear change (2) via a transfer chain sprocket (38), a chain (42) and a driven transfer chain sprocket (40), said third sun wheel being designed to rotate by a integral with said third pinions using a friction element (C3), said third sun wheel being selectively connected with a friction element (B3) to serve as a reaction element, and connected to a one-way clutch (F2) so not to rotate in the same direction as said motor,   said fourth solar wheel (60) receiving the output of said second satellite carrier.   9. Power transmission train of an automatic transmission for a vehicle comprising: a transmission casing for installing said automatic transmission; a torque converter for changing the speed of the engine power torque; a shell cover for containing said torque converter; a first gear change section of a compound planetary gear unit (2) comprising first and second simple planetary gear units mounted on an input shaft for performing a first gear change operation, said first gear unit simple sun gear comprising a first sun wheel (18) surrounded by and engaged with a plurality of first pinions (16) supported by a first planet carrier, a first sun gear ring (12) surrounding and internally engaged with said first pinions, and a hub (14) connected to said first planetary gear ring (12), and said second single planetary gear unit comprising a second sun wheel (24) surrounded by and   io engaged with a plurality of second pinions (22) supported by a second holder   satellites, and a second planetary gear ring (26) surrounding and internally engaged with said second pinions (22); a second gear change section of a single planetary gear unit (4) comprising third (44) and fourth (46) simple planetary gear units for performing a second gear change operation, said third planetary gear unit simple comprising a third sun wheel (52) surrounded by and engaged with a plurality of third pinions (50) supported by a third planet carrier, and a third ring of planetary gear (48) surrounding and engaged therein with said third pinions (50), and said fourth single planetary gear unit comprising a fourth sun wheel (60) surrounded by and in engagement with a plurality of fourth pinions (62) supported by a fourth planet carrier (58), and a fourth planetary gear ring (66) surrounding and engaging therein with said fourth pinions; a plurality of power transfer elements (32, 34) for transferring power from said motor; and a differential gear (D) for transferring the output of said second gear change section to an axle (68) of the vehicle, wherein said third sun gear (48) receives the output of said first gear change section via a transfer chain sprocket (38), a chain (42) and a driven transfer chain sprocket (40), said third sun wheel selectively serving as a reaction element, said fourth planetary gear ring gear (66) being connected to said third planet carrier and said fourth wheel 23 2723777   solar (60) being fixedly connected to said transmission housing (56) to serve of reaction element.   10. An automatic transmission power transmission train for a vehicle comprising: a transmission casing (56) for installing said automatic transmission; a torque converter (TC) for changing the speed of the engine power torque; a shell cover (6) for containing said torque converter; a first speed change section of a compound planetary gear unit (2) comprising first and second simple planetary gear units mounted on an input shaft to perform a first gear change maneuver, said gear unit simple sun gear comprising a first sun wheel (18) surrounded by and engaged with a plurality of first pinions (16) supported by a first planet carrier, a first sun gear ring (12) surrounding and internally engaged with said first pinions, and a hub (14) connected to said first planetary gear ring gear, and said second single planetary gear unit comprising a second sun wheel (24) surrounded by and engaged with a plurality of second pinions (22) supported by a second planet carrier, and a second ring of planetary gear (26) surrounding and engaged inside with said second pinions; a second gear change section of a single planetary gear unit (4) comprising a third (44) simple planetary gear unit for performing a second gear shifting operation, said third simple planetary gear unit comprising a third wheel solar (52) surrounded by and in   taken with a plurality of third pinions (50) supported by a third holder   satellites (58), and a third planetary gear ring (48) surrounding and engaging therein with said third pinions (50); and a differential gear (D) for transferring the output of said second gear change section (2) to an axle (68) of the vehicle, wherein said third sun gear (48) receives the output of said first gear section gear change (2) via a drive transfer chain sprocket (38), a chain (42) and a driven transfer chain sprocket (40), said third sun wheel being designed to serve selectively as a reaction element. 11. Power transmission train of an automatic transmission for a vehicle comprising: a transmission casing (56) for installing said automatic transmission; a torque converter (TC) for changing the speed of the engine power torque; a shell cover (6) for containing said torque converter; a first gear change section of a compound planetary gear unit (2) comprising first and second simple planetary gear units mounted on an input shaft (8) for performing a first gear change operation, said first single planetary gear unit comprising a first solar wheel (18) surrounded by and engaged with a plurality of first   pinions (16) supported by a first planet carrier, a first gear ring gear -   planetary (12) surrounding and internally engaged with said first pinions, and a hub (14) connected to said first planetary gear ring (12), and said second single planetary gear unit comprising a second sun wheel (24 ) surrounded by and   engaged with a plurality of second pinions (22) supported by a second holder   satellites, and a second planetary gear ring (26) surrounding and internally engaged with said second pinions; a second gear change section of a single planetary gear unit (4) comprising third (44) and fourth (46) simple planetary gear units for performing a second gear change operation, said third planetary gear unit simple comprising a third sun wheel (52) surrounded by and engaged with a plurality of third pinions (50) supported by a third planet carrier (58), and a third planetary gear ring (48) surrounding and engaged interior with said third pinions, and said fourth single planetary gear unit comprising a fourth sun wheel (60) surrounded by and engaged with a plurality of fourth pinions (62) supported by a fourth planet carrier (64), and a fourth planetary gear ring (66) surrounding and internally engaged with said fourth pinions; a plurality of power transfer elements (32, 34) for transferring power from said motor; and a differential gear (D) for transferring the output of said second gear change section to an axle (68) of the vehicle, wherein said third planet gear ring receives the output of said first gear change section through the through a driven transfer chain sprocket (40), said third sun gear being connected to said transmission case to serve selectively as a reaction element, said fourth sun wheel (60) being connected to said third planet carrier ( 58), and said fourth planet gear ring gear (66) being connected to said transmission case (56) to serve essentially as a reaction element. 12. Power transmission train of an automatic transmission Is for a vehicle comprising: a transmission casing (56) for installing said automatic transmission; a torque converter (TC) for modifying the power torque speed of the motor; a shell cover (6) for containing said torque converter; a first gear change section of a compound planetary gear unit (2) comprising first and second simple planetary gear units mounted on an input shaft (8) for performing a first gear change operation, said first single planetary gear unit comprising a first sun wheel (18) surrounded by and engaged with a plurality of first pinions (16) supported by a first planet carrier, a first planetary gear crown (12) surrounding and engaged at the interior with said first pinions, and a hub (14) connected to said first planetary gear ring gear, and said second single planetary gear unit comprising a second sun wheel (24) surrounded by and in   taken with a plurality of second pinions (22) supported by a second holder   satellites, and a second planetary gear ring (26) surrounding and internally engaged with said second pinions; a second gear change section of a single planetary gear unit (2) comprising third (44) and fourth (46) simple planetary gear units for performing a second gear change operation, said third planetary gear unit simple comprising a third sun wheel (52) surrounded by and engaged with a plurality of third pinions (50) supported by a third planet carrier (58), and a third planetary gear ring (48) surrounding and engaged interior with said third pinions, and said fourth single planetary gear unit comprising a fourth sun wheel (60) surrounded by and engaged with a plurality of fourth pinions (62) supported by a fourth planet carrier (64), and a fourth planetary gear ring (66) surrounding and internally engaged with said fourth pinions; a plurality of power transfer elements (32,34) for transferring the power of said motor; and a differential gear (D) for transferring the output of said second gear change section to an axle (68) of the vehicle, wherein said third sun wheel (52) receives the output of said first gear change section by l through a driven transfer chain sprocket (40), said third sun gear (48) being connected to said transmission case to selectively act as a reaction member, said fourth sun gear (66) being connected to said third planet carrier (58), and said fourth sun wheel (60) being connected to said transmission case (56) to serve essentially as a reaction element.